Alignment apparatus

Abstract

An alignment apparatus for positioning on a wafer an image of a mask formed by a projection optical system. The apparatus includes a first detecting system for detecting the distance between an imaging plane of the optical system and the wafer, a driving mechanism for moving the wafer in the direction of the optical axis of the optical system and a second detecting system for detecting the amount of movement of the wafer. The driving mechanism is controlled while the distance detected by the first detecting system is compared with the amount of movement detected by the second detecting system, whereby the wafer is correctly and accurately positioned on the imaging plane of the optical system.

What is claimed is: 
     
       1. An apparatus for aligning an object with an imaging plane of an optical system, comprising: a first detecting means for detecting the position of the object with respect to the imaging plane of the optical system;   displacement means for changing the positional relation of the object relative to the imaging plane of the optical system;   a second detecting means for detecting the amount of change in the positional relation of the object relative to the imaging plane of the optical system by said displacement means; and   control means for controlling said displacement means on the basis of the results of detection by said first and second detecting means, said control means comparing sequentially the results of detection by said first and second detecting means with each other and controlling said displacement means so that the results of detection by said first and second detecting means co-ordinate with each other.   
     
     
       2. An apparatus according to claim 1, wherein said second detecting means includes an eddy current type position detector. 
     
     
       3. An apparatus according to claim 2, wherein said displacement means includes an electrostrictive element. 
     
     
       4. An apparatus according to claim 3, wherein said first detecting means includes an air-microsensor. 
     
     
       5. An apparatus according to claim 4, wherein said control means includes a processing means for generating a signal corresponding to the difference between the result of detection by said first detecting means and that detected by said second detecting means, comparing means for binarizing a sawtooth wave signal on the basis of the signal produced by said processing means, and switching means for controlling charging/discharging of said electrostrictive element in accordance with an output from said comparing means. 
     
     
       6. An alignment apparatus comprising: an electrostrictive element;   detecting means for detecting the amount of change in said electrostrictive element; and   control means for controlling charging/discharging of said electrostrictive element on the basis of the difference between the amount of change detected by said detecting means and a predetermined set amount.   
     
     
       7. An apparatus according to claim 6, wherein said control means includes a first circuit at a lower voltage for obtaining the difference between the amount of change detected by said detecting means and the predetermined set amount, and a second circuit at a higher voltage for executing charging/discharging of said electrostrictive element. 
     
     
       8. An apparatus according to claim 7, wherein said control means includes a photo-coupler for transmitting an output of said first circuit to said second circuit. 
     
     
       9. An apparatus according to claim 8, wherein said first circuit includes an operational amplifier for generating a signal corresponding to the difference between the amount of change detected by said detecting means and the predetermined set amount, and a comparator for binarizing a sawtooth wave signal on the basis of the signal produced by said operational amplifier. 
     
     
       10. An apparatus according to claim 9, wherein said second circuit includes a plurality of transistors which are adapted to be controlled on the basis of the output from said photo-coupler. 
     
     
       11. An apparatus according to claim 6, wherein said control means includes a pulse generating circuit for producing a pulse signal for controlling charging/discharging of said electrostrictive element, and a duty changing circuit for changing the duty in the pulse signal produced by said pulse generating circuit. 
     
     
       12. An apparatus for aligning a flat object with an imaging plane of an optical system, comprising: a plurality of first detecting means, each of said first detecting means detecting the position of the object with respect to the imaging plane of the optical system;   a plurality of displacement means, each of said displacement means changing the positional relation of an associated portion of the object relative to the imaging plane of the optical system;   a plurality of second detecting means, each of said second detecting means detecting the amount of change in the positional relation between an associated portion of the object relative to the imaging plane of the optical system by an associated one of said displacement means, independently from the change by the remaining displacement means; and   control means for controlling each of said plural displacement means individually on the basis of the result of detection by an associated one of pairs of said first and second detecting means.   
     
     
       13. An apparatus according to claim 12, wherein the apparatus includes the same number of said plural first detecting means, said plural second detecting means and said plural displacement means. 
     
     
       14. An apparatus according to claim 13, wherein each of said second detecting means detects directly the amount of change by an associated one of said displacement means. 
     
     
       15. An apparatus according to claim 14, wherein each of said displacement means includes an electrostrictive element. 
     
     
       16. An apparatus according to claim 15, wherein each of said second detecting means includes an eddy current type position detector.